Rosetta update: Both "big burns" completed successfully

Rosetta is now in the final phase of its approach to comet 67P/Churyumov-Gerasimenko after a decade-long journey. Usually, when you steer a spacecraft to a planet, you can use the planet's gravity to help capture you into orbit. But a comet is so lacking in mass that it provides no help to your navigation. In order for Rosetta to enter orbit, the spacecraft has to do all the work to precisely match the size, shape, and orientation of its orbit to the comet's. The final phase of the approach includes a series of rocket burns to brake Rosetta to the right speed. The two largest burns have now succeeded, and Rosetta reported this morning via Twitter that the second burn was close to perfect.

Date

PlannedDelta-v(m/s)

ActualDelta-v(m/s)

Midpoint of burn(UTC)

ROS/67P dist(km)

Relative velocity(m/s)

May 7

20

20

16:45

1,918,449

775.1

May 21

290.89

289.59

19:08

1,005,056

754.1

June 4

269.5

269.49

17:48

425,250

463.0

June 18

90.76

14:31

194,846

192.1

July 2

58.80

12:57

51,707

101.3

July 9

24.91

11:57

22,314

43.0

July 16

10.65

11:12

9,590

18.4

July 23

4.62

10:30

4,126

7.9

Rosetta is now closing on the comet at a rate of about 17,000 kilometers per day, and is less than 300,000 kilometers away. The comet started showing activity, growing a coma, in April, so I had hoped to accompany this update with some new photos of the increasingly large coma. Alas, ESA has released no images; their media relations team didn't respond to a question I sent them yesterday about when we might expect more. So the only photos I have to show you are the ones I posted a month ago. I know they have images, because they use them for optical navigation.

Comet Churyumov-Gerasimenko develops a coma, March 27 to May 4, 2014

A sequence of images showing comet 67P/Churyumov–Gerasimenko moving against a background star field in the constellation Ophiuchus between 27 March and 4 May 2014, as the distance between the spacecraft and comet closed from around 5 million to 2 million kilometers. The comet (and Rosetta) were between 640 million km and 610 million km from the Sun during the sequence. The comet is seen to develop a dust coma as the sequence progresses, with clear activity already visible in late April. Exposure times are 720 seconds for each image, taken with the OSIRIS Narrow Angle Camera. The globular cluster M107 is also clearly visible in the field of view.

When should Rosetta start actually resolving the comet as a disk? The Rosetta OSIRIS Narrow Angle Camera has pixels that are 0.0186 milliradians across. The comet has a nucleus about 4 kilometers across. The nucleus should subtend one pixel when Rosetta is about 200,000 kilometers away. Rosetta will close to that distance at about the same time as the next rocket burn on June 18. It takes more than one pixel to start resolving details on the nucleus, though. Maybe when it's about 10 pixels across we'll start discerning a lump here or a bump there. That won't happen until the second week of July. I can't wait to see what it looks like! I hope they show us some photos.

Comments:

Congo Recluse: 06/10/2014 11:16 CDT

I think the narrow angle camera g=has a pixel resolution of 0.0186 'milli' radians rather than 'micro' radians. Single pixel resolution of the comet would be achieved at 215 million km distance otherwise and we would already being enjoying spectacular views. Still things are looking to get very interesting, very quickly, very soon.

Mark Zambelli: 06/10/2014 01:00 CDT

My question is this... given the second burn came in with slightly less delta-v and the third burn was near perfect, when are we likely to see the introduction of a longer burn to compensate? Is it better to wait for a few burns to see what happens or to start adjustments right-away?

Emily Lakdawalla: 06/10/2014 01:08 CDT

Congo: You're right! I fixed the error, thanks for pointing it out.
Mark: They already cleaned up the teeny amount of error in the first burn during the second burn; you'll likely see all the planned burn lengths change over time as they fine-tune their approach.

Mark Zambelli: 06/10/2014 02:20 CDT

Thanks Emily, didn't spot if the burn-lengths were being amended in those lists so thankyou for pointing that out. Makes perfect sense to correct with each subsequent burn, thanks.

david: 06/10/2014 03:22 CDT

Thanks Emily. Hope they show us pictures next time. ESA really need to improve public affair office...

stone: 06/11/2014 02:03 CDT

The copy right of the images is not with ESA, but with the PI of the instrument. So ESA has only limited possibilities. Look for the Halley image of Giotto of the HMC it is still tied to the PI and the institution he worked with and not ESA.

PeterG: 06/11/2014 03:58 CDT

At a recent Rosetta mini-symposium in Amsterdam I noticed that ESA is enthusiastic about the degree of public outreach achieved so far with Rosetta.
Building on this positive trend, I asked one of the Rosetta project managers whether routine navigation-purpose pics could be made available quickly - in the same way that immediate sharing of raw pics from Mars is boosting public outreach without impinging on formal news releases/papers.
I tried to leverage their outreach success to date: please, please.. continue even stronger and try to remove the sharp edges of your well-established 6 month embargo for PI’s.. See fantastic results in UMSF and other internet places if you need to be convinced..
“Body language” answer: we fully understand.. we know about UMSF.. not immediately, but perhaps from Q1 2015 onwards??
In a way, fair enough I think. The initial tracking and sighting (of details-) of the comet after an epic journey is certainly frontpage stuff and anything but routine. So let’s hope for the best!
PS
At the symposium I was awed by the incredible challenge that the Rosetta mission really is. Do you realize it is 1993-vintage hardware, comms… I found I had to adjust my –too high- expectation level which was unconsiously influenced by smooth 3rd generation ops on Mars. Maybe a good subject for a couple of future Rosetta-blogs by the engineers involved. As one mentioned to me: this will really be rocket science!